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摘要
The present manuscript reports the novel synthesis of ultrathin graphene sheets employing malonic acid as a reducing agent (GRH-MA) under mild pH conditions. AFM reveals their thickness to be 0.41 +/- 0.03 nm. XPS of GRH-MA exhibits the increased intensity of the C] C band suggesting the effective reduction of graphene oxide (GO) with enhanced sp(2) character. Optical, infrared and Raman spectroscopy, the increased C/O ratio in FESEM and TEM analysis also support this observation. Current-voltage (I-V) measurements show about four orders of magnitude higher conductivity for GRH-MA (4.4 S cm(-1)) as compared to that of GO (3.05 x 10(-4) S cm(-1)). The reduction of GO by oxalic acid (GRH-Ox) under identical experimental conditions was observed to be less efficient as indicated by optical and Raman spectroscopy, and I-V measurements. The efficient reduction by malonic acid is thus understood by the presence of the active methylene group, which makes it an effective nucleophile. XRD of GRH-MA sheets annealed at 300 degrees C (GRH-MA300) exhibits the %26apos;d%26apos; spacing of 0.35 nm. HRTEM analysis of GRH-MA300 also showed a similar %26apos;d%26apos; spacing of 0.35 +/- 0.01 nm with a hexagonal structure, indicating the formation of a more ordered graphitic structure upon annealing. IR analysis of this sample exhibited a significant reduction in the oxygen functionalities and I-V measurements showed a more than 4-fold increase in conductivity as compared to that of GRH-MA. In cyclic voltammetry, GRH-MA shows a fairly high specific capacitance (Cs) of 173 F g(-1) which is more than 23-fold higher to that of GO (7.5 F g(-1)) at 100 mV s(-1) in 1 M H2SO4. Galvanostatic charge-discharge measurements show the maximum Cs value of 254 F g(-1) at 1 A g(-1) which is more than an order of magnitude higher to that of GO (18.6 F g(-1)) and 1.25 times higher to that of GRH-Ox (202 F g(-1)), respectively. Moreover, 1000 cycles of charge-discharge at 10 A g(-1) exhibit fairly good cyclic stability demonstrating its immense potential for energy storage applications.
- 出版日期2014
